Pin UX changes (bug 842861, bug 848525)

This branch addresses the majority of the UX around ping entry as per bug 842861 and fixes the display of the forgotten password button (now a link) to not be shown in the reset flows: (bug 848525)

The remaining issues are:

* Dealing with the locked pin flow as per spec (bug 856150)
* Progress overlays are still needing to be implemented (will raise a bug for that)
* Workaround for the re-paint issue when entering pin or backspacing pin entry (840117)